Topic of the Moment – Proton Beam Therapy

As Ashya King begins to receive proton beam therapy for a brain tumour, we look at what the treatment is and how it works.

Credit: Shutterstock/Crystal Eye Studios

Five-year-old Ashya King found himself at the centre of controversy after being removed from a Southampton hospital in August, with his parents set on seeking proton beam therapy overseas.

Proton beam therapy works similarly to conventional radiotherapy, except that beams of protons, instead of X-rays, are used to kill cancer cells.

Both high-energy electromagnetic waves and charged particles can constitute ionising radiation because of the effect they have when passing through a substance – stripping electrons from atoms. When this happens in biological tissue, it can break up the DNA inside cells, leaving the cells unable to multiply.

Using protons for the task has several advantages over X-rays for treating cancer. Because of their mass, protons are easier to keep focused into a tight beam targeted accurately on the tumour that they’re intended to destroy. They also have a certain range, beyond which they are unlikely to penetrate further into the body, and deposit most of their energy within a few millimetres of that range.

Compared to X-rays, protons are much easier to concentrate on cancer cells while limiting the damage caused to nearby healthy tissue.

Proton therapy was first suggested as a possible way to treat cancer by nuclear physicist Robert R Wilson in 1946, and the first treatments were carried out – using particle accelerators originally built for research – a decade later.

The first facility in the UK began operation in Liverpool in 1989 – a low-energy version only used to treat tumours in the eye. Two advanced radiotherapy centres offering high-energy proton beam therapy are set to open in 2018.